This is not that complicated
So, don't go to the Air Inc conference. Now, let's say it's five years later and you still don't have that dream job. Will you regret, then, that you didn't go? If you want a job in the airline industry, then do everything possible to get the job--it's that simple. As a side note, I personally know one person that got an interview at NetJets by attending--and that person was subsequently hired. Also, since you asked, I recommend the interview seminar. Unless you're an interview olympian, you need the advice. Don't get me wrong--Air Inc is not the Alpha and Omega of your job search--it's just one of many things you should do to cast your wide net. Yes, it's going to cost you a few bucks, but you should realistically plan to spend $8-10K on your job search--this conference is part of it. Good luck!
Before the flamers attack, yes, yes, lots of people get airline jobs by spending much less than $10K, but plan on it anyway...you'll spend that much on a crappy car!